The present invention pertains to a controllable hydraulic bearing for motor vehicles with a working chamber and an equalizing chamber arranged annularly around the working chamber, which are filled with an electrorheological fluid and are connected to one another via an annular gap-like overflow channel, wherein the overflow channel has two mutually opposite electrodes for generating a high-voltage field in the overflow channel.
Such an engine bearing of this type has been known, e.g., from the documents DE 41 22 360 and DE 196 17 83. Controllable hydraulic bearings are used to obtain damping properties adapted to different operating conditions with a single hydraulic bearing. The fluid is usually moved to and fro between the working chamber and the equalizing chamber via the overflow channel located between the two chambers as a consequence of vibrations acting on the hydraulic bearing. The to-and-fro movement of the fluid has a vibration-damping effect especially at low frequencies and correspondingly high amplitudes. The location and the extent of the maximum possible damping (resonance frequency) is determined by the parameters channel length, channel cross section and fluid viscosity. Since both the channel length and the channel cross section are given in a prior-art hydraulic bearing, the frequency and the amplitude of the maximum damping can be changed only by changing the viscosity of the fluid used. Special substances, called electrorheological fluids, have been known for this purpose in the prior art, in which the application of an electric field causes a change in viscosity. The change in viscosity takes place here in proportion to the intensity of the electric field applied, the reaction of the fluid taking place in the millisecond range.
However, it was found in practice that the intensity of the electric fields necessary for a change in viscosity within the overflow channel provided with electrodes requires very high voltages because, on the one hand, a narrow gap is to be provided between the mutually opposite electrodes for a change in viscosity, but, on the other hand, a narrow gap leads to a low fluid throughput within the overflow channel, as a result of which the damping properties of the hydraulic bearing in question are in turn affected adversely as a consequence of the small amount of fluid. A relatively long overflow channel with a corresponding small gap, in which an annular gap electrode and a counterelectrode can build up a corresponding high-voltage field, is proposed in the design variant disclosed as a solution in DE 196 17 839. However, the fact that a great overall height of the hydraulic bearing must be accepted due to the length of the overflow channel is a major drawback of the solution disclosed.
The object of the present invention is therefore to further improve a hydraulic bearing of this type such that there is a corresponding small gap in the overflow channel and a sufficient length is available at the same time for providing the amount of fluid necessary for good damping properties, but the dimensions of the hydraulic bearing according to the present invention shall be at the same time compact, the design shall be simple to ensure a high level of reliability of operation, and manufacture shall be inexpensive.
According to the present invention, the overflow channel extends helically in its longitudinal extension (or as a spiral) around the working chamber between this working chamber and the equalizing chamber, and the wall of the channel consists of an electrically insulating carrier layer, which is provided with electrode-forming, conductive cover layers on both sides.
Due to the helical design of the overflow channel according to the present invention, an especially long channel can be obtained in a very small space, and the gap between the mutually opposite walls of the overflow channel can be selected at the same time to be particularly small. The helical winding of the channel walls additionally achieves the goal of the present invention that the electrically conductive cover layer applied to each side of the wall of the channel automatically generates an opposite charge of the mutually opposite channel walls at a positive or negative charge. Thus, an electric voltage field, which can lead to a variation in the viscosity of the fluid present in the overflow channel, can be generated in a very simple manner by applying a voltage to one cover layer.
It proved to be particularly expedient to design the carrier layer and the conductive cover layers as a one-part, flexible laminate strip. Such a flexible strip can be manufactured in a simple manner and can be handled without problems in terms of the manufacturing technology. An especially inexpensive design of the hydraulic bearing according to the present invention is obtained, furthermore, if each laminate strip forming the walls of the overflow channel is accommodated on its narrow side in an insulating plate, wherein a groove, which corresponds to the spiral shapes of the overflow channel and which is engaged by the respective upper and lower narrow sides of the laminate strip, is recessed in the insulating plates. The two insulating plates, e.g., ones made of a ceramic material, make unnecessary an additional insulation of the two cover layers located on the laminate strip after the installation; in addition, the flexible laminate strip is reliably fixed in the grooves recessed in the insulating plates.
The connection of the cover layers arranged on both sides of the carrier layer, which is necessary for the application of electric energy, is preferably embodied by an electric connection each arranged on the outside of the hydraulic bearing.
An exemplary embodiment of the subject of the present invention will be explained in greater detail below on the basis of the drawings attached.